Site difference influence of anchored Ru in mesoporous carbon on electrocatalytic performance toward pH-universal hydrogen evolution reaction

Ru-based electrocatalysts have demonstrated excellent electrocatalytic performance toward hydrogen evolution reaction (HER). However, designing Ru nanoparticles/nanoclusters (Ru NPs/NCs) with abundant accessible active sites is challenging. Herein, a selective facile hydrothermal in situ polymerization strategy is described to accurately control the anchoring point of Ru in hollow mesoporous carbon spheres (HMCs) (outer surface, HMCs@Ru; cavity, Ru@HMCs; and pore channels, Ru/S-HMCs). The HER mechanisms of the three catalysts over a wide pH range were revealed by analyzing the loading position, content, dispersion, particle size, and valence state of Ru. HMCs@Ru shows excellent area activity, with overpotentials of 64.3, 2.8, and 78.1 mV at 10 mA·cm −2 in 0.5 mol⋅L −1 H 2 SO 4 , 1 mol⋅L −1 KOH, and 0.5 mol⋅L −1 phosphate buffer saline (PBS) solutions, respectively. Ru/S-HMCs exhibit high mass activity, with values 43.3, 2.9, and 12.7 times those of Pt/C in alkaline, acidic, and neutral media, respectively, at − 50 mV (vs. reversible hydrogen electrode (RHE)). After 2000 cyclic voltammetry cycles, the performances of HMCs@Ru and Ru/S-HMCs hardly decrease, indicating good stability. The excellent electrocatalytic activity can be attributed to two main factors: (1) the confinement effect, which not only promotes high Ru dispersion but also prevents the leaching of active metal under harsh conditions, and (2) their excellent structural characteristics. The catalyst structure features a large hollow located in the center (~ 160 nm in diameter) and an ultrathin monolayer of mesopores (~ 6 nm) uniformly distributed on the hollow shells, ensuring fast mass diffusion and electron transfer kinetics, as well as complete accessibility of catalytic sites. Graphical abstract